1. Field of the Invention
The present invention relates to a method of and an apparatus for continuously performing hydrothermal synthesis using a material slurry and an aqueous liquid.
2. Description of the Prior Art
The rate of reaction of numerous oxides, such as silica and alumina, with high-pressure water vapor, particularly water heated to a temperature not lower than a critical temperature, becomes higher in the presence of high temperature water, particularly high-pressure and high-temperature water. For this reason, hydrothermal synthesis using such a phenomenon is widely practiced.
Currently, the art of effecting hydrothermal synthesis of particles under pressurized conditions exceeding a critical pressure (Tp=218.3 atm) in a temperature region exceeding a saturated vapor temperature, particularly a temperature region exceeding a critical temperature (Tc=374.degree. C.), is carried out by a batch system. However, a large batch system requires long temperature rising and falling times in addition to the time required to retain a desired temperature and pressure after the setting of a material. In addition, because of batch production, the efficiency of synthesis in one apparatus is limited.
A method of continuously feeding and processing a slurry in a piping assembly is disclosed in, for example, Japanese Patent Laid-Open No. 53-57112, but this method is not directed to the hydrothermal synthesis of particles. Another method, which is disclosed in Japanese Patent Publication No. 2-5136 is carried out below a saturated aqueous vapor pressure. Yet another method, which is disclosed in PCT International Publication No. WO 93/00304 (Japanese National Publication No. 511190/1994), is intended to decompose organic substances, but is not intended to synthesize particles. In other words, there have not yet been continuous manufacturing techniques which are capable of performing hydrothermal synthesis of particles, reducing the temperature and pressure, and discharging the synthesized particles, by means of a piping which is assembled to retain a pressurized state at a temperature exceeding a critical temperature.
The present invention is intended to realize continuous hydrothermal synthesis in a pressurized state at a high temperature by solving problems, such as the problem of how to feed a material slurry, the problem of retaining the inside of a pipe in a high-temperature pressurized state, the problem of how to take out synthesized particles, and the problem of how to clean the inside of the apparatus after operation, these problems having been experienced in a case where a hydrothermal synthesis reaction is integrally carried out in a continuous piping by using as a synthesis region the cross-hatched region of the state-of-water diagram shown in FIG. 3.